Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.80   11.846%   $230.1791   $230.18   $230.20   $230.20  
  Purchase #2 $192.57   13.514%   $218.5939   $218.59   $218.60   $218.60  
  Purchase #3 $39.99   10.297%   $44.1078   $44.11   $44.10   $44.10  
  Purchase #4 $114.85   12.747%   $129.4899   $129.49   $129.50   $129.50  
  Purchase #5 $82.85   3.794%   $85.9933   $85.99   $86.00   $86.00  
  Purchase #6 $154.77   5.115%   $162.6865   $162.69   $162.70   $162.70  
  Purchase #7 $135.55   11.838%   $151.5964   $151.60   $151.60   $151.60  
  7 purchase totals = $926.38       $1,022.6469   $1,022.65   $1,022.70   $1,022.70